Modem aircraft typically include a great number of sensors, effectors, etc., connected to an avionics network having a central processor. The sensors, effectors, etc. are typically line replaceable units (LRUs) to improve operational effectiveness. The LRUs are typically concentrated at particular locations in the aircraft where systems are installed. To reduce wiring, and therefore weight, a remote data concentrator (RDC) may be used to connect several of the LRUs to the avionics network.
To reduce design and manufacturing costs, and to improve operational effectiveness, all of the RDCs on a particular aircraft may be standardised, regardless of the LRUs to which they are connected. The RDCs may therefore have common hardware, and so are known as common remote data concentrators (cRDCs). The cRDCs may include configurable software. Standardisation of the cRDC makes it possible to hold an inventory of fewer parts, such that a defective cRDC can be readily replaced during routine maintenance tasks, thereby improving operational effectiveness.
The RDCs are connected to the aircraft power distribution by power bus bars. For redundancy, commercial airliners typically have at least two independent bus bars, one running along each side of the aircraft fuselage. Each bus bar has the capacity to carry all power to/from the RDCs in the event of failure of an entire side of the avionics architecture. For greater redundancy an aircraft may have more than two bus bars, some of which are emergency bus bars to replicate the two main bus bars.
Traditional avionics architecture design rules have required complete segregation between the bus bars, and redundancy for each LRU. Segregation is required to prevent failure propagating from one bus bar to the other. Therefore, for any given LRU, e.g. a sensor, connected via an RDC to one bus bar there needs to be an identical, redundant LRU connected via another RDC to the other bus bar. Modern sensors/effectors are very reliable, sometimes more so than the avionics network to which they are connected. If a particular aircraft sensor/effector is deemed to be sufficiently reliable (low sensitivity) then it may be possible to design the avionics architecture such that that particular sensor/effector has no redundant pair. However, there remains the problem that a single sensor/effector still needs to be connected to both bus bars on each side of the aircraft, and these bus bars must still be completely segregated.
An alternative “non-standard” approach is to design the RDC with a “double lane” architecture, whereby a single sensor/effector connected to an RDC is linked to either the first bus bar, or the second bus bar, at any instance with mechanical relay switching between the two. The mechanical switching relay can satisfy the requirements for isolating the two bus bars, whilst providing a reduction in the number of sensors/effectors and RDCs on the aircraft, giving considerable weight saving and reduced emissions. However, this “double lane” architecture for the RDC is non-standard and each RDC generally has to be designed differently according to its location and connections on the aircraft. The considerable benefits of a flexible, simplex, integrated modular electronics architecture (IMA) using cRDCs cannot therefore be realised.